Potentiometer



D. A. PRETOT POTENTIOMETER I Jan. 23, 1968 Filed Feb. 4, 1966 INVENTOR. @077 /4., 1 /19/02 2M 4 WZ- 3,365,6hh Patented Jan. 23, 1968 Fire 3,365,690 POTENTHQMETER Don A. Pretot, El Cajon, Calif assignor to California General, Zine, Chuia Vista, Califi, a corporation of California Filed Feb. 4, 1966, Ser. No. 525,234 6 Claims. (Cl. 338143) ABSTRACT OF THE DHSCLGS A potentiometer unit is described in the following specification which may be housed, for example, in a tubular housing and mounted on a control panel, or the like. The potentiometer comprises an insulating rod having screw threads, and with an insulating wire and a low resistance return wire wrapped around the screw threads. The resistance wire and return wire are bridged by a torsion type wiper which, in turn, is carried by a wiper nut, the latter being driven along the threaded insulating rod.

The present invention relates to variable resistors, and it relates more particularly to an improved potentiometer in which a movable contact is driven around a helically Wound resistance element.

In the embodiment of the invention to be described, an elongated rod-like insulating member has a helical screw thread formed along its length. The return conductor rail, or wire, of the potentiometer is wound around the major diameter of the member in a helical path, and is bonded thereto. The return wire is mechanically afiixed to one end of the rod, and it is electrically connected to a terminal pin at the other end.

The resistance element of the potentiometer is wrapped around the minor diameter of the insulating rod in a helical path and is also bonded thereto. One end of the resistance element is connected to a second terminal pin which, like the first terminal pin, extends through the base of the assembly. The other end of the resistance element is connected to a bus conductor which extends through a passage extending lengthwise through the insulating rod. The other end of the bus is connected to a third terminal pin, which, likewise, extends through the base.

A wiper nut is driven along the threaded insulating member, and it carries a torsion type wiper. The wiper is in the form of an electrically conductive Wire, and it moves along the resistance element and the return rail, in a manner to be described, so as to function as the movable contact of the potentiometer.

The aforesaid threaded insulated rod may be composed, for example, of a suitable plastic. For example, a thermoplastic such as that marketed by the Du Pont Company under the trade name Delron, may be used. The wiper nut may be composed of a suitable plastic, for example, such as Teflon.

The screw threads of the threaded rod and of the wiper nut may be slightly mismatched, so that the nut is always held in a tight fit with respect to the rod. This is to avoid backlash or play in the potentiometer.

An object of the invention, therefore, is to provide an improved variable resistor of the wire-wound potentiometer type; and to provide one which may be calibrated with a high degree of precision, and which may exihibit precise linear characteristics.

Another object of the invention is to provide such an improved variable resistor which is relatively inexpensive to construct, and yet which is rugged and accurate in its operation, and is able to Withstand shocks and rough usage.

Yet another object of the invention is to provide such an improved variable resistor which exhibits no measurable backlash, even after long periods of use, and which is not subject to wear or deterioration.

A still further object of the invention is to provide such an improved variable resistor which is small in size and light in weight.

The features of the invention which are believed to be new are set forth expressly in the claims. The invention, itself, however, together with further objects and advantages, may best be understood by reference to the following description, when the description is taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a side sectional view of the assembly of the present invention in one of its embodiments;

FIGURE 2 is a side perspective view of the assembly, with the casing partly broken away to expose the manner in which the drive fork engages the wiper nut of the assembly; and

FIGURE 3 is a fragmentary sectional view showing the relationship between the wiper nut and a threaded rod in the assembly.

The improved variable resistor, or potentiometer, of the present invention, insofar as the illustrated embodiment is concerned, is encased in a tubular housing 10. The housing It may be composed, for example, of aluminum or any other appropriate substance.

A header or base 1L2 having a disc-like con-figuration encloses one end of the housing iii. The housing may be fixed to the head 12 by screws, or other appropriate means. The header 12 may be composed, for example, of any appropriate insulating material, such as thermosetting plastic.

An elongated rod-like insulating member 14 is mounted on the header 12, and the member 14 extends along the length of the assembly within the housing It). The member 14 has a rod-like configuration, and is composed of a suitable insulating material, such as Delron, as explained above. A helical thread is formed in the rod 14, and, as shown, the thread extends the length of the rod.

A groove is formed in the major diameter of the rod 14, and this groove follows a helical path along the length of the rod. A conductor 16 is wound in the groove about the major diameter, and this conductor extends the length of the rod 14, as shown. The conductor 16 constitutes the return rail for the assembly. The end 16a of the conductor 16 is bonded into the material of the rod 14 so as to be rigidly fixed to the rod. The other end of the conductor 16 is soldered, or otherwise attached to the head of a terminal pin 18 by means, for example, of a solder joint 19. The terminal pin 18 extends through the header 12, as shown.

A resistance element 20 is wound about the minor diameter of the rod 16. This resistance element may, for example, be in the form of a resistance wire.

In a particular constructed embodiment of the invention, the rod 14 was wound with ten turns of resistance wire. The overall resistance of the unit was 10 ohms to within i1%. Also, the linearity of the particular unit was Within l%.

The resistance of the assembly can easily be increased, by replacing the resistance wire by a resistance coil. For the latter purpose, a circular channel may be formed at the bottom of the threads of the rod 14 in the helical path around its minor diameter.

One end of the resistance element 16 is soldered or otherwise connected to a pin 22 by means, for example, of a solder joint 24. The right hand end of the resistance element 25 is soldered, or otherwise connected to a bus which passes through a passageway (not shown) in the rod 1-4. The passageway is displaced, for example, to one side of the center of the rod. It is usual to insert a relatively low resistance conductor bus into the passageway, and to solder the end of the resistance element to the end of that conductor (as mentioned). The other end of the bus conductor is soldered, for example, to pin 3% by way of a solder joint 3-2.

A Wiper nut 36 of insulating material is threaded to the rod 14. As mentioned above, the threads of the nut 36 are mismatched slightly with the threads of the rod 14, so as to maintain a tight fit between the nut and the rod and to avoid backlash. It will also be observed that the teeth of the nut 36 do not extend directly to the minor diameter of the rod 14, so that there is no rubbing between the nut and the resistance element Also, the return conductor 16 does not extend beyond the surface of the major diameter of the rod 14, so that there is no rubbing between the nut and the conductor 16. The nut 36, as mentioned above, may be composed of an appropriate plastic material, such as Teflon.

A wiper element 38, which is in the form of an electrically conductive pin, is embedded in the nut 36, and extends through the nut in the manner shown in FIGURE 1. The pin 38 is electrically conductive, and it is in the form of a torsion bar. A first end portion 38a of the pin extends into rubbing relationship with the return conductor rail 16. It will be appreciated that the portion 38a of the pin extends longitudinally with respect to the portion 16 so that the wiping action is with the grain and abrasion is reduced to a minimum. Also, there is no tendency for spring hysteresis to afiect the operation of the wiper pin.

The other end portion 38b of the wiper pin 38 engages the resistance element 20 in the threads of the rod 14. Again, the engagement is longitudinal in the same manner in which the portion 38a engages the return rail 16.

The drive element for the wiper nut 36 is in the form of a fork 40. The tines of the fork 40 extend through holes in the wiper nut in slidable relationship therewith. A drive shaft 42 extends through the end of the housing 10, and this drive shaft has a transverse coupling member 44 integral with one end thereof and which engages the intermediate portion of the fork 40. As the drive shaft 42 is rotated, the fork 40 also rotates, causing the nut 46 to rotate. The nut then travels along the rod 14 and, at the same time, slides along the fork 40.

It will be appreciated that the sliding relationship between the drive fork 40 and the wiper nut 36 causes the wiper nut to the unaffected by any vibrations of the shaft 42 in a longitudinal direction.

A post 48 may be formed on the end of the rod 14 to engage the intermediate portion of the fork 40. This post can serve as a thrust bearing for the unit, and no ball bearings or other expensive journaling means are required in the assembly.

Adjustable stops can be provided for the wiper nut 36, merely by threading nuts onto the arms of the fork 40 on one side or both sides of the wiper nut 36. These stop nuts can then be adjusted, so as to stop the wiper nut at any desired position.

While a particular embodiment of the invention has been described, modifications may be made. It is intended to cover in the claims all modifications which come within the scope of the invention.

What is claimed is:

1. A potentiometer including: a base; an elongated rodlike insulating member mounted on said base and having a helical thread formed therein with a first helical groove in the major diameter of said rod and a second helical groove in the minor diameter of said rod; a conductor constituting a return rail for the potentiometer wound in one of said grooves; a resistance wire wound in the other of said grooves; a first terminal member connected to said conductor; second and third terminal members respectively connected to the ends of said resistance wire; a wiper nut threaded on said rod; an electrically conductive pin extending through said nut and configured to have a first end portion extending longitudinally with respect to said conductor in rubbing engagement therewith and to have a second end portion extending longitudinally with respect to said resistance wire in rubbing engagement therewith; and a fork-like drive member for said wiper nut having tines extending through holes in said wiper nut in sliding relationship therewith.

2. The potentiometer defined in claim 1, and which includes a tubular housing enclosing said rod-like insulating member and affixed to said base at an open end thereof; and which includes a drive shaft rotatably mounted at the end of said housing remote from said base and coupled to said fork-like drive member.

3. The potentiometer defined in claim 1, in which said terminal members are in the form of electrically conductive pins extending through said base.

4. The potentiometer defined in claim 3, and which includes an electrical conductor extending lengthwise through said rod-like insulating member and connecting one end of said resistance wire to one of said pins.

5. The potentiometer defined in claim l, in which said wiper nut and said rod-like member are configured so that said wiper nut is spaced from said return rail and said resistance wire so as to obviate any rubbing action between said wiper nut and said return rail and said resistance wire.

6. The potentiometer defined in claim 2, and which includes a post on the end of said rod-like member remote from said base, the intermediate portion of said fork-like drive member extending across said post in a thrust-bearing relationship therewith; and in which said drive shaft is rotatably mounted in said remote end of said housing in spaced axial relationship with said rod-like member; and which includes a transverse coupling member affixed to the inner end of said shaft and engaging said intermediate portion of said fork-like drive member.

References Cited UNITED STATES PATENTS 2,938,396 5/1960 Nicolosi et a1 33-8143 X 2,978,662 4/1961 Bell 338143 3,069,646 12/1952 Hardison et al 338-143 3,108,244 10/1963 Nirenberg et a1. 338-148 X ROBERT K. SCHAEFER, Primary Examiner.

H. HOHAUSER, Assistant Examiner, 

